Electronic device and method for manufacturing the same

ABSTRACT

An Al film is formed on a cap wafer and the Al film is patterned into a ring-shaped film. Dry etching is performed by using the ring-shaped film as a mask to form a drum portion enclosing a recess portion to provide a vacuum dome. After forming a depth of cut into the substrate portion of the cap wafer, the cap wafer is placed on a main body wafer having an infrared area sensor formed thereon. Then, the ring-shaped film of the cap wafer and the ring-shaped film of the main body wafer are joined to each other by pressure bonding to form a ring-shaped joining portion.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to electronic devices, such assensors and transistors, configured to be sealed in an atmosphere ofreduced pressure or an atmosphere of inert gas.

[0002] Conventionally, electronic devices exhibiting high performance inan atmosphere of vacuum (or atmosphere of reduced pressure), such asinfrared sensors and vacuum transistors, are typically sealed in a caseof hermetic seal and ceramic or the like for use thereof. Suchvacuum-packaged electronic devices include a so-called discrete type ofdevice having a single sensor disposed therein and an integration typeof device having a large number of sensors and transistors arranged inan array-like configuration.

[0003] On the other hand, it has been suggested to provide a smallerhighly-integrated semiconductor device by sealing sensors, emittingelements or the like arranged in an array-like configuration into anatmosphere of vacuum, but not into a special case of ceramic or thelike, by a packaging method employing a process for manufacturingsemiconductor devices. For example, the official gazette ofinternational publication No. WO 95/17014 describes a method for sealinga cell array-arranged area into a vacuum atmosphere. Therein, after acell array of detectors for infrared radiation or the like or a cellarray of emitting elements is formed on a first wafer, a second wafer isthen placed on the first wafer with a predetermined spacing left betweenthem, and the wafers are joined to each other by solder at the peripheryof the cell array while the space between both the wafers is maintainedunder atmosphere of vacuum.

[0004] However, the technique described in the above official gazettehas following problems.

[0005] First, when a large number of elements such as infrared detectorsare arranged in an array-like configuration, it is difficult to make thewhole joining portion at the periphery of the cell array completelyflat, and thus an excessively high push pressure is inevitably requiredfor thermal pressure bonding, thereby causing the possibility of brokenwafers during joining, deteriorated vacuum caused by residual stress anddevice malfunctions.

[0006] Second, if a joining failure is caused at part of the joiningportion for maintaining elements such as a large number of infrareddetectors under vacuum, the vacuum is broken over the whole cell array,and thus the whole device becomes bad, thus resulting in a high percentdefective.

[0007] Third, when solder is used for the joining, the degree of vacuumin the inside space having the cell array placed therein can not behigher than a certain level because of outgassing of organic materialsincluded in the solder paste. Therefore, there has been the possibilitythat an increase in the sensitivity of infrared sensors can be nothoped, for example.

SUMMARY OF THE INVENTION

[0008] A first object of the present invention is to provide anelectronic device suitable for miniaturization and integration and amethod for manufacturing it, by taking measures that seals theelectronic device in an atmosphere of pressure-reduced or an atmosphereof inert gas in the unit of the area in which detectors for infraredradiation or the like and electron emitting elements are disposed.

[0009] A second object of the present invention is to improve thefunction of electronic devices such as infrared sensors, by takingmeasures for providing a higher degree of vacuum in the inside space inwhich an cell array is placed.

[0010] The electronic device according to the present inventioncomprises a main body substrate having a plurality of cell regions inwhich at least one element is disposed, a cap body placed on the abovedescribed main body substrate, a cavity portion provided in a positionhaving said element disposed therein and being located in at least onecell region of the above described plurality of cell regions, enclosedby the above described main body substrate and the above described capbody, and maintained in an atmosphere of reduced pressure or in anatmosphere of inert gas, and a ring-shaped joining portion providedbetween the above described main body substrate and the above describedcap body for isolating the above described cavity portion from externalspace.

[0011] Thereby, an element such as an infrared sensor and electronemission element or the like can be individually disposed in a cavityportion, which element requires an atmosphere such as an atmosphere ofreduced pressure and an atmosphere of inert gas isolated from externalspace. Thus, it is possible to provide a structure suitable for both adiscrete type of electronic device and an integration type of electronicdevice having a large number of elements integrated therein.

[0012] The electronic device further comprises a first ring-shaped filmformed on the above described main body substrate and enclosing theabove described element, and a second ring-shaped film formed on theabove described cap body, wherein the above described ring-shapedjoining portion is formed between the above described first and secondring-shaped films. Thereby, it is possible to provide a strongring-shaped joining portion by selecting the material configuring thefirst and second ring-shaped films.

[0013] The materials of the above described first and second ring-shapedfilms are preferably selected from at least any one of In, Cu, Al, Au,Ag, Ti, W, Co, Ta, Al—Cu alloy, and an oxide film.

[0014] The materials of the above described first and second ring-shapedfilms are the same material with each other.

[0015] The above described main body substrate is configured bysemiconductor, and the above described element on the above describedmain body substrate and an external circuit are electrically connectedto each other through an impurity-diffused layer formed in the abovedescribed main body substrate to extend across the above describedring-shaped film. Thereby, it is possible to permit an improvement inthe reliability of the electrical connection between the above describedelement and the external circuit.

[0016] The above described cap body is provided with a recess portionfor forming the above described cavity portion and a drum portionenclosing the recess portion, and the above described main bodysubstrate is provided with a engagement portion for engaging with theabove described drum portion. Thereby, it is possible to provide anelectronic device having a stable position connection between the mainbody substrate and the cap body and the high reliability of the joining.

[0017] The above described electronic device is preferably an elementselected from any one of an infrared sensor, pressure sensor,acceleration sensor and vacuum transistor.

[0018] If the above described electronic device is an infrared sensor,the element provided on the above described main body substrate is athermoelectric transducer element.

[0019] In this case, the above described cap body has a Si substrate anda semiconductor layer provided on the Si substrate and having a band gapof less than 1.1 eV. Thereby, it is possible to avoid thesuperimposition of background signals caused by light near visiblelight, and therefore a large dynamic range can be ensured for infrareddetection, thus providing an electronic device suitable for detecting ahuman and an animal.

[0020] In this case, the top layer of the above described cap body isconfigured by a Si layer having a diffraction pattern formed thereon toprovide a Fresnel lens. Thereby, it is possible to focus infraredradiation on the thermoelectric transducer element in the infraredsensor, thus permitting an improvement in the efficiency of detectinginfrared radiation.

[0021] The above described electronic device is preferably an infraredsensor having a thermoelectric transducer element, a support member forsupporting the above described thermoelectric element, and a secondcavity portion formed below the above described support member.

[0022] In this case, a pillar or a wall extending from the abovedescribed support member is not provided in the above described secondcavity portion. Thereby, it is possible to permit an improvement in thesensitivity of detecting infrared radiation and an improvement in thedetection accuracy.

[0023] Also, the above described second cavity portion is configured tocommunicate with the described cavity portion. Thereby, it is possibleto permit an improvement in the sensitivity of detecting infraredradiation and an improvement in the detection accuracy.

[0024] The above described ring-shaped joining portion is provided morethan one in number to enclose the above described plurality of cellregions. Thereby, it is possible to provide an integration type ofelectronic device.

[0025] A first method for manufacturing an electronic device accordingto the present invention comprises a step (a) of preparing a main bodysubstrate having a plurality of cell regions in which at least oneelement is disposed and a cap substrate, and forming a plurality ofrecess portions each enclosing at least one cell region of the abovedescribed plurality of cell regions on at least any one of the abovedescribed main body substrate and the above described cap substrate, anda step (b) of forming a ring-shaped joining portion such that at leastpart of recess portions of the above described plurality of recessportions may remain as cavity portions isolated from external spacebetween the above described main body substrate and the above describedcap substrate, by applying a push pressure between the above describedmain body substrate and the above described cap substrate.

[0026] According to this method, it is possible to manufacture either ofa discrete type of electronic device and an integration type ofelectronic device by using an existing process such as a Si process orthe like. In addition to this, since the cavity portions are formed withthe cap bodies individually placed on each cell region, even if ajunction failure occur in part of the cell regions, the other cellregions are practically usable. Therefore, it is possible to permit animprovement in yield in both a discrete type and an integration type.

[0027] In the above described step (a), a plurality of first and secondring-shaped films enclosing the above described recess portions areprepared on the above described main body substrate and cap substrate,respectively, and in the above described step (b), the above describedring-shaped joining portion is formed between the above described firstand second ring-shaped films. Thereby, it is possible to form a strongring-shaped joining portion by selecting the material of the first andsecond ring-shaped films.

[0028] The above described step (b) is performed with the joining usinghydrogen bonding and a metallic bond or with room temperature joining,and thus it is possible to reliably isolate the cavity portion fromexternal space.

[0029] The above described step (a) is preferably performed by usingmaterial selected from at least any one of In, Cu, Al, Au, Ag, Ti, W,Co, Ta, Al—Cu and an oxide film as the materials of said first andsecond ring-shaped films.

[0030] It is preferable that as the materials of the above describedfirst and second ring-shaped films, the same material is used to bothfilms.

[0031] The above described step (b) is performed without heating theabove described main body substrate and the above described capsubstrate to a temperature of not less than 450° C., thereby it ispossible to perform the joining without causing damage to Al wiring.

[0032] In the above described step (a), a slit for partitioning theabove described cap substrate into a plurality of areas is formed in theabove described cap substrate, thereby when the first and second filmsare joined to each other by the application of a push pressure, even ifthe wafer is warped, it is possible to suppress the occurrence ofjunction failures caused by local large stress.

[0033] In the above described step (a), by forming recess portionsenclosed by the above described each second ring-shaped film and aplurality of drum portions enclosing the recess portions on the abovedescribed cap substrate, the recess portions need to be formed only inthe above described cap substrate. Thereby, it is possible to avoiddifficult process steps of manufacturing the main body substrate.

[0034] The above described step (a) prepares the above described mainbody substrate having an engagement portion for engaging with the drumportion of the above described cap substrate. Thereby it is possible torealize an improvement in the accuracy of aligning the first and secondring-shaped films to each other, and thus to provide an electronicdevice that is highly reliable in the joining.

[0035] The above described step (b) is preferably performed in anatmosphere of reduced pressure, or in an atmosphere of inert gas.

[0036] The above described step (b) is performed in an atmosphere ofreduced pressure having a pressure of higher than 10⁻⁴ Pa. Thereby, itis possible to avoid the difficulty of holding a high vacuum, thusrealizing the joining that is practical and suitable for massproduction.

[0037] By further including a step of breaking the above described mainbody substrate into each cell after the above described step (b), adiscrete type of electronic device can be obtained.

[0038] A method for manufacturing a second electronic device comprises astep (a) of preparing a main body substrate having a plurality of cellregions in which at least one element is disposed and a cap substrate,and forming recess portions enclosing the above described plurality ofcell regions in at least one of the above described main body substrateand the above described cap substrate, and a step (b) of forming aring-shaped joining portion with the joining using hydrogen bonding or ametallic bond or with room temperature joining by applying a pushpressure between the above described main body substrate and the abovedescribed cap substrate, wherein in the above described step (b), theabove described ring-shaped joining portion is formed such that at leasta portion of the above described recess portions may remain as cavityportions isolated from external space in the above described pluralityof cell regions.

[0039] By this method, compared to the use of solder joining, it ispossible to increase the function of holding the atmosphere in thecavity under a predetermined atmosphere. For example, For an electronicdevice to which an atmosphere of high vacuum is preferable, it ispossible to hold the cavity portion under an atmosphere of high vacuum.

[0040] In the above described step (a), a first ring-shaped filmenclosing a plurality of cell regions is formed on the above describedmain body substrate and a second ring-shaped film having approximatelythe same pattern as said first ring-shaped film is formed on the abovedescribed cap substrate, and thereby it is possible to realize strongjoining by selecting materials forming first and second ring-shapedportions.

[0041] The above described step (a) is preferably performed by using atleast any one material selected from the group of In, Cu, Al, Au, Ag,Ti, W, Co, Ta, Al—Cu and an oxide film as the materials of the abovedescribed first and second ring-shaped films.

[0042] In this case, as the materials of the above described first andsecond ring-shaped films, the same material is preferably used to bothfilms.

[0043] The above described step (b) can be performed without heating theabove described main body substrate and the above described capsubstrate to a temperature of not less than 450° C.

[0044] The above described step (a) can be performed such that all cellregions disposed on one electronic device may be enclosed by the abovedescribed first and second ring-shaped films.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]FIGS. 1A to 1D are cross-sectional views for schematically showingan example of basic structure of an electronic device according to thepresent invention.

[0046]FIGS. 2A to 2D are cross-sectional views for schematically showingexample structures of a joining portion for maintaining the electronicdevice of the present invention under vacuum.

[0047]FIGS. 3A and 3B are a plan view and a cross-sectional view forshowing an example of an electrical connection structure suitable forthe electronic device of the present invention, respectively.

[0048]FIGS. 4A and 4B are a cross-sectional view and an electricalcircuit diagram of an infrared sensor according to the presentinvention, respectively.

[0049]FIGS. 5A to 5F are cross-sectional views for showing process stepsfor manufacturing an infrared sensor according to the present invention.

[0050]FIGS. 6A to 6E are plan views for showing process steps forforming a bolometer and the peripheral area thereof.

[0051]FIGS. 7A to 7F are cross-sectional views for showing a cap bodyused for an infrared sensor according to Embodiment 1.

[0052]FIG. 8 is a cross-sectional view for schematically showing aconfiguration of an apparatus used for pressure bonding.

[0053]FIG. 9 is an electrical circuit diagram for illustrating aconfiguration of an infrared area sensor according to Embodiment 2 ofthe invention.

[0054]FIG. 10 is a timing chart for showing a method for controlling theinfrared area sensor of Embodiment 2.

[0055]FIGS. 11A to 11F are perspective views for showing a process formanufacturing an infrared area sensor having a cell array according toEmbodiment 2.

[0056]FIG. 12 is a cross-sectional view for showing an example of amicro vacuum transistor having a vacuum dome structure according toEmbodiment 3 of the present invention.

[0057]FIG. 13 is a cross-sectional view for showing the whole structureof the infrared sensor according to Embodiment 1 and embodiment 2 of thepresent invention.

[0058]FIG. 14 is a cross-sectional view for showing the whole structureof the infrared sensor according to Embodiment 4 of the presentinvention.

[0059]FIG. 15 is a cross-sectional view for showing the whole structureof the infrared sensor according to an example variation of the fourthembodiment 4 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0060] (Basic Structure of an Electronic Device)

[0061]FIGS. 1A to 1D are cross-sectional views for schematically showingan example of basic structure of an electronic device according to theinvention. The concrete structure of an element disposed in a cellregion 11 in the electronic device as shown in FIGS. 1A to 1D will bedescribed later.

[0062] At least a cell-disposed portion of the cell region 11 ismaintained in an atmosphere of vacuum by a cap body. The elementprovided on the cell region may include an infrared sensor, pressuresensor, acceleration sensor, rate-of-flow sensor, vacuum transistor, orthe like.

[0063] Infrared sensor can be divided into two broad categories: athermal type of sensor such as a bolometer, pyroelectric sensor, andthermopile, and a quantum type of sensor using PbS, InSb, HgCdTe, or thelike. Some bolometers use polycrystalline silicon, Ti, TiON, VO_(x) orthe like. Some thermopiles use the Zeebeck effect induced at PNjunction, and some of the other use the transient characteristics of aforward current flowing through PN diode or the like. Some pyroelectricinfrared sensors use a change in dielectric constant of materials suchas PZT, BST, ZnO, and PbTiO₃. A quantum type of infrared sensor detectsa flow of current produced by electron excitation. These infraredsensors in general have characteristics improved when sealed in anatmosphere of vacuum or an atmosphere of inert gas within a cap body.

[0064] For pressure sensors and acceleration sensors, it is known thattheir characteristics are improved when they are sealed in an atmosphereof vacuum or inert gas by a cap body, because the sensitivity thereof isimproved when the viscosity resistance of air is reduced.

[0065] Also, the number of elements disposed in one cell region ofsensors of these types may be one or plural. Further, a switchingelement (transistor) may be provided in the cell region together with anelement having characteristics improved by a higher degree of vacuum, asrequired.

[0066] —First Example of Basic Structure—

[0067] As shown in FIG. 1A, an electronic device according to the firstexample of basic structure comprises a main body substrate 10 formed ofa Si wafer, and a cap body 20A formed of a Si wafer for sealing adesired area of the main body substrate 10 in an atmosphere of reducedpressure. The main body substrate 10 is provided with a cell region 11in which a single element such as an infrared sensor and a circuit forsending signals to the element are disposed. On the other hand, the capbody 20A comprises a substrate portion 21 of silicon and a drum portion22 enclosing a recess portion to provide a cavity portion 23 held in theatmosphere of vacuum. That is, by using various joining methodsdescribed later, a portion of the cell region of the main body substrate10 and the drum portion 22 of the cap body 20A are joined to each otherto form a ring-shaped joining portion 15 for sealing the cavity portion23 to be held in the atmosphere of reduced pressure. Thereby, aconfiguration has been made to permit the elements in the cell region 11to exhibit a desired function.

[0068] Herein, the structure of the recess portion includes one spaceformed by etching and removing a portion of the flat substrate to agiven depth and another space enclosed with the drum portion configuredby a closed-loop-like wall existing on the flat substrate. FIG. 1Adiscloses only a recess portion configured by the space enclosed withthe drum portion 22. However, according to the invention, the structureof the recess portion formed in the main body substrate or in thesubstrate for use in the cap or in both the substrates before the cavityportion is formed is not limited to the form shown in FIG. 1A. This isthe same in each example of basic structure and in each embodiment, asdescribed below.

[0069] Also, as the methods for forming a drum portion enclosing therecess portion, one method removes the other region except for aclosed-loop-like region left in a flat substrate to a given depth toform a drum portion, and another method builds up a closed-loop-likewall on a flat substrate to form a drum portion. Both the methods may beused for the invention.

[0070] —Second Example of Basic Structure—

[0071] As shown in FIG. 2B, a cap body 20B in an electronic deviceaccording to the second example of basic structure comprises a Ge filterportion 24 of Ge having a thickness of 3 μm, in addition to thesubstrate portion 21 and the drum portion 22 enclosing a recess portionto provide the cavity portion 23 held in an atmosphere of reducedpressure. The main body substrate 10 in the second example of basicstructure has the same structure as the main body substrate 10 in thefirst example of basic structure. In this case, the substrate portion 21easily transmits light of a wavelength not shorter than about 0.8 μm(infrared light). In contrast to this, the Ge filter portion 24 cantransmit only light of a wavelength not shorter than about 1.4 μm(infrared light) and shields a wavelength range, near to visible light,having wavelengths not longer than 1.4 μm.

[0072] Therefore, by applying the second example of basic structure to adevice having an infrared sensor built in the cell region 11, it ispossible to prevent false detection resulting from a change in theamount of current flowing through transistors or the like which changeis caused by the incidence of light near to visible light. This iseffective because infrared sensors are particularly used for detectinghuman bodies and animals during the night and light near to visiblelight from cars and illumination may excite carriers in the activeregion of transistors in electronic circuits, thus causing a reductionin a detection margin due to superimposition of background signals.

[0073] Also, in order to epitaxially grow a layer of Ge on a siliconwafer, after epitaxially growing layers of Si_(1-x)Ge_(x) on the siliconwafer such that the Ge component ratio x may change from 0 to 1, a Gelayer of a predetermined thickness can be epitaxially grown thereon.

[0074] By the way, after layers of Si_(1-x)Ge_(x) are epitaxially grownon the Ge layer such that the Ge component ratio x may change from 1 to0, a Si layer can be epitaxially grown thereon by a predeterminedthickness. If the processs thereafter are advanced with the Ge layerexposed, it is fear that the manufacturing apparatuses may becontaminated by Ge, and if the surface layer is configured by a Silayer, a process for manufacturing electronic devices can be applied tothe next processing for forming Fresnel lens. From these points of view,the Ge layer is preferably not exposed on a top surface.

[0075] Also, the layer functioning as a filter may be configured by amaterial including elements other than Ge. Particularly, materialshaving a narrower band-gap than that of Si 1.1 eV can absorb light inthe range of wavelengths longer than 0.8 μm (mainly near infraredlight), and thus can avoid problems caused by carries excited inimpurity-diffused layer of transistors or the like disposed in cells.

[0076] —Third Example of Basic Structure—

[0077] As shown in FIG. 1C, an electronic device according to the thirdexample of basic structure have a cap body 20C which comprises a Gefilter portion 24 and a Si layer having a grating pattern 27 engraved inthe surface thereof, which pattern provides a Fresnel lens having thefunction of a convex lens, in addition to the substrate portion 21 andthe drum portion 22 enclosing a recess portion to provide the cavityportion 23 held in an atmosphere of reduced pressure. The structure ofthe main body substrate 10 in the third example of basic structure isthe same as the structure of the main body substrate 10 in the firstexample of basic structure. For the same reason as in the second exampleof basic structure, the third example of basic structure is suitable fora device having an infrared sensor built therein, and particularly itcan effectively focus light on the existing position of a resistancebody by using the function of a concave lens provided by grating patternon the surface thereof. Therefore, the third example can provide anelectronic device suitable for miniaturization and higher performance.

[0078] In the earth's atmosphere, there is wavelength regions called“atmospheric windows” at the wavelength ranges of electromagnetic wavesof 3 μm to 5 μm and 8 μm-10 μm, which have high transmission factor forinfrared radiation. Although infrared radiation of these regions passesthrough the atmosphere, wavelength ranges except for the atmosphericwindow is difficult to detect due to disturbance noises. Further, theinfrared radiation emitted from human bodies and the bodies of animalshas a wavelength range of 3 μm-10 μm. Therefore, the provision of a Gefilter layer 24 permits infrared sensors to accurately detect targethumans and animals, while avoiding false detection caused by light inthe range of 0.8 μm-1.4 μm near to visible light.

[0079] In addition, instead of the Ge filter, a SiGe filter (compositionSi_(1-x)Ge_(x)) may be provided. In this case, a frequency band ofinfrared radiation to be removed is shifted in the range of 0.8 μm-1.4μm according to the component ratio x of Ge. For this reason, theprovision of a SiGe filter provides an advantage that a cutoff frequencyband can be adjusted as desired.

[0080] —Fourth Example of Basic Structure—

[0081] As shown in FIG. 1D, an electronic device according to the fourthexample of basic structure comprises the main body substrate 10 formedof Si, and a cap body 20D formed of Si for sealing a desired area of themain body substrate 10 in an atmosphere of reduced pressure. The mainbody substrate 10 is provided with a large number of cell regions 11 inwhich one element such as an infrared sensor and a circuit for feedingsignals to the element are disposed. On the other hand, the cap body 20Dcomprises the substrate portion 21 and a large number of the drumportions 22 for enclosing a recess portion to provide the cavity portion23 held in an atmosphere of reduced pressure. That is, by using variousjoining methods described later, a portion of each cell region 11 of themain body substrate 10 and each drum portion 22 of the cap body 20D arejoined to each other in an atmosphere of reduced pressure to form aclosed-loop-like ring-shaped joining portion 15. Thereby, each cavityportion 23 is held in the atmosphere of reduced pressure, and thus aconfiguration is made to allow the elements in each cell region 11 toexhibit a desired function.

[0082] Further, a depth of cut for partitioning the substrate portion 21into each cell region is provided in the substrate portion 21, and thusthe substrate portion 11 is separately divided at the depth-of-cutportion during joining or after joining. However, it may be not dividedat the depth-of-cut portion. In this case, the configuration is madesuch that the push pressure applied on the joining portion in each cellcan be made as uniform as possible by elastic deformation induced at thedepth-of-cut portion, even if delicate differences in the push pressure(force for pressure bonding) can be caused by the different thickness ofjoining portion of each cap body and the deformation of the wafer tendto cause.

[0083] Also, in FIG. 1D, although the cap body 20D has only thesubstrate portion 21, it may comprise a Ge cap portion. In addition, itmay comprise a lens function such as a Fresnel lens on the surfacethereof.

[0084]FIGS. 1A to 1D illustrates the joining between the main bodysubstrate and the cap body as realized by Si to Si junction. However,generally, use of the metal to metal junction can make the manufacturingprocess easier than the Si to Si junction. Thus, hereinafter, examplestructures of joining portion will be described.

[0085] (Example Structures of Joining Portion)

[0086]FIGS. 2A to 2D are cross-sectional views for schematically showingexample structures of the joining portions for holding the electronicdevice of the invention under vacuum.

[0087] Here, the meanings of the joining using hydrogen bonding, thejoining using metallc bonds and the room temperature joining which areused in the invention will be described.

[0088] The hydrogen bonding is made under a low pressure of the rangefrom normal pressure to 10⁻⁴ Pa and with heating in some cases andwithout heating in other cases. The metallic bonds are made under theapplication of pressure to about 1000 Pa in some cases and under aultra-low vacuum lower than 10⁻⁸ Pa in other cases. Further, themetallic bonds are made by heating at high temperature in some cases andby not heating. In the room temperature joining, the materials to bejoined are directly joined to each other at an atomic level withoutheating. This joining is performed in the range from a relatively lowvacuum of about 10⁻⁴ Pa to an ultra-low vacuum of a pressure lower than10⁻⁸ Pa. The room temperature joining can join materials to be joinedexcept for metal to each other, such as a metal to metal, ceramic toceramic, and silicon to silicon junction. Also, the room temperaturejoining includes direct joining at an atomic level (performed in therange of 10⁻⁶-10⁻⁹) and joining using metallic bonds.

[0089] —First Example Structure of the Joining Portion—

[0090] As shown in FIG. 2A, in the first example structure, aring-shaped film 12 of a joining material of metal (for example,aluminum (Al)) is provided on the main body substrate 10, and aring-shaped film 26 of a joining material of metal (for example, Al) isprovided on the end of the drum portion 22 of the cap body 20. Thus,ring-shaped films 12 and 26 are joined to each other in an atmosphere ofreduced pressure by using hydrogen bonding or the like to form thering-shaped joining portion 15, thereby sealing the cavity portion 23 onthe cell region 11 under an atmosphere of reduced pressure.

[0091] Also, in the first example structure of the joining portion andthe second-fourth example structures of the joining portion describedlater, joining materials of metal includes, in addition to Al, metalssuch as In, Cu, Au, Ag, Ti, W, Co, Ta, and Al—Cu alloy, or alloys. It ispossible to use metal to metal, metal to alloy, and alloy to alloymetallic bonds among these metals and alloy. Further, materials otherthan metal may be used as the joining material. For example, it ispossible to use silicon oxide film-silicon oxide film, silicon oxidefilm-Si, and Si—Si hydrogen bonding.

[0092] When making the joining using these metallic bonds and hydrogenbonding or the room temperature joining, the joining can be easily madeunder an atmosphere of low temperature and low vacuum according to theinvention. At this point, these joining can be said to be suitable forthe invention.

[0093] Further, in the first example structure of the joining portionand the second-fourth example structures of the joining portiondescribed later, each ring-shaped film 12, 26 does not need to isprovided to use Si to Si hydrogen bonding.

[0094] —Second Example Structure of the Joining Portion—

[0095] As shown in FIG. 2B, in the second example structure of thejoining portion, a ring-shaped protrusion portion 14 of an insulatingfilm is provided on the main body substrate 10, and a ring-shaped film12 is provided on the cell region 11 within the ring-shaped protrusionportion 14 in the cell region. On the other hand, the ring-shaped film26 is provided on the end of the drum portion 22 of the cap body 20.Thus, in an atmosphere of reduced pressure, the ring-shaped films 12 and26 are bonded to each other to form the ring-shaped joining portion 15,while the drum portion 22 is being fitted into the ring-shapedprotrusion portion 14. Thereby, the cavity portion 23 on the cell region11 is sealed in an atmosphere of reduced pressure. That is, thering-shaped protrusion portion 14 functions as an engagement portion forengaging with the drum portion 22. However, although the main bodysubstrate 10 is provided with a recess portion having the inside surfaceengaging with the outside surface of the drum 22, the outside surface ofthe engagement portion of the main body substrate may be engaged withthe inside surface of the drum portion 22.

[0096] Since this example structure of the joining portion ensures thatthe cap body 20 can be fixed on the main body substrate 10, it is astructure suitable for an electronic device having a plurality of cellregions 11.

[0097] —Third Example Structure of the Joining Portion—

[0098] As shown in FIG. 2C, in the third example structure of thejoining portion, a ring-shaped protrusion portion 14 configured by ainsulation material having the tapered inside surface is provided on themain body substrate 10, and a ring-shaped film 12 is provided on thecell region 11 within the ring-shaped protrusion portion 14 in the cellregion. On the other hand, the outside surface of the drum portion 22 ofthe cap body 20 is formed into a tapered surface having the same slopeas the tapered inside surface of the ring-shaped protrusion portion 14,and further the ring-shaped film 26 is provided on the end of the drumportion 22. Thus, in an atmosphere of reduced pressure, the ring-shapedfilms 12 and 26 are joined to each other to form the ring-shaped joiningportion 15, while the inside surface of the ring-shaped protrusionportion 14 is being fitted on the outside surface of the drum portion22. Thereby, the cavity portion 23 on the cell region 11 is sealed in anatmosphere of reduced pressure. In this case, the ring-shaped protrusionportion 14 also functions as an engagement portion engaging with thedrum portion 22. However, a recess portion having the inside surfaceengaging with the outside surface of the drum portion 22 may be providedin the main body substrate 10 as the engagement portion. Also, theoutside surface of the engagement portion of the main body substrate maybe engaged with the inside surface of the drum portion 22.

[0099] According to this example structure of the joining portion, thecap body 20 can be easily aligned on the main body substrate 10, andthus it is a structure particularly suitable for an electronic devicehaving a plurality of cell regions 11.

[0100] —Fourth Example Structure of the Joining Portion—

[0101] As shown in FIG. 2D, in the fourth example structure of thejoining portion, a ring-shaped protrusion portion 14 configured by of ainsulation material having the stepped inside surface is provided on themain body substrate 10, and a ring-shaped film 12 is provided on thecell region 11 within the ring-shaped protrusion portion 14 in the cellregion. On the other hand, the outside surface of the drum portion 22 ofthe cap body 20 is formed into a stepped surface which can engage withthe stepped inside surface of the ring-shaped protrusion portion 14, andfurther the ring-shaped film 26 is provided on the end of the drumportion 22. Thus, in an atmosphere of reduced pressure, the ring-shapedfilms 12 and 26 are joined to each other to form the ring-shaped joiningportion 15, while the inside surface of the ring-shaped protrusionportion 14 is being fitted into the outside surface of the drum portion22. Thereby, the cavity portion 23 on the cell region 11 is sealed in anatmosphere of reduced pressure.

[0102] In this case, the ring-shaped protrusion portion 14 alsofunctions as an engagement portion engaging with the drum portion 22.However, a stepped outside surface may be provided on the outside of thedrum portion 22 and a recess portion having the inside surface engagingwith this stepped outside surface may be provided in the main bodysubstrate 10 as the engagement portion. Also, a stepped inside surfacemay be provided inside the drum portion 22 and thus the engagementportion having the stepped outside surface engaging therewith may beprovided on the main body substrate.

[0103] According to this example structure of the joining portion, thecap body 20 can be easily aligned on the main body substrate 10, andthus it is a structure particularly suitable for an electronic devicehaving a plurality of cell regions 11.

[0104] (Electrical Connection Structure)

[0105]FIGS. 3A and 3B are a plan view and a cross-sectional view forshowing an electrical connection structure suitable for the electronicdevice according to the invention, respectively. Herein, FIG. 3A is aplane structure of the electronic device with its cap body removed.

[0106] As shown in FIGS. 3A and 3B, the main body substrate 10 and thecap body 20 are mechanically connected to each other by the joiningbetween ring-shaped films 12 and 26, and the cavity portion 23 is formedbetween both of them. Also, on the main body substrate 10, an element 40shown by a broken line such as a bolometer and a N channel type ofswitching transistor 30 having a gate electrode 31, source region 32 anda drain region 33 are provided. This switching transistor 30 controlsthe electrical connection between the element 40 and an externalcircuit. Thus, the electrical connection between the element 40 disposedon the area sealed by the cap body 20 and the external circuit areon-off controlled. The drain region 33 and gate electrode 31 of thisswitching transistor 30 are provided in the area enclosed by the capbody 20. As shown in FIG. 3A, the source region 32 is formed in the mainbody substrate 10 to extend across each ring-shaped film 12, 26. Also,in the area located directly below the drum portion of the cap body 20,there are provided impurity-diffused layers (N+ type diffused layer) 32,35 and 36 for functioning as wiring, which are formed so as to crosseach ring-shaped film 12 and 26 in the main body substrate 10.

[0107] Also, an interlayer insulating film 41 of silicon oxide coveringthe switching transistor 30 and the main body substrate 10 and apassivation film 42 covering the interlayer insulating film 41 areformed above the main body substrate 10. Further, on the main bodysubstrate 10, there are provided a contact 31 a for establishing aconnection between the gate electrode 31 of the switching transistor 30and the impurity-diffused layer 36, a first wiring 51 a for connectingthe source region of the switching transistor 30 and an external circuit(not shown) to each other, a second wiring 51 b for connecting theimpurity-diffused layer 36 and an external circuit (not shown) to eachother, a third wiring 51 c for connecting the drain region 33 of theswitching transistor 30 and the element 40 to each other, a fourthwiring 51 d for connecting the element 40 and the impurity-diffusedlayer 35 to each other, and a fifth wiring 51 e for connecting theimpurity-diffused layer 35 and an external circuit (not shown) to eachother. That is, the element 40 and the switching transistor 30 areconnected through the third wiring 51 c and the drain region 33. Also,the element 40 is connected to an external circuit through the fourthwiring 51 d, the impurity-diffused layer 35 and the fifth wiring 51 e.

[0108] By choosing such an electrical connection structure, no metalwiring is present directly below the ring-shaped joining portion 15existing between the ring-shaped film 26 of the cap body 20 and thering-shaped film 12 of the main body substrate 10. Therefore, it ispossible to effectively prevent the wiring from being ruptured andbroken by a push pressure (pressure bonding force) for establishing thejunction between the ring-shaped films, and to prevent the reliabilityof connection from being deteriorated due to the wiring partiallyruptured by the pressure. Also, since the interlayer insulating film 41can be easily covered by the passivation film 42 within the cavityportion 23, it is possible to prevent gas or the like generated from theinterlayer insulating film 41 from entering into the cavity portion 23,thereby permitting the cavity portion 23 to be held in a good vacuum.

[0109] Further, the external circuit may be formed in an area on themain body substrate not covered by the cap body 20, or may be providedin an area different from the area in which an infrared sensor isprovided.

[0110] Also, in the structure of the electronic device shown in FIGS. 3Aand 3B, the cap body 20 is provided so as to enclose the element 40 andswitching transistor 30 (particularly drain region 33) in the cellregion. Therefore, by mounting a Ge layer having a filter function onthe cap body 20, it is possible to avoid the occurrence of possibleproblems caused by the carriers excited in the drain region of theswitching transistor 30 in the cell region. Also, Instead of providing aGe layer on the cap body 20, a filter of Ge or the like may be providedat any appropriate position where the filter can prevent the incidenceof light into the switching transistor 30. Further, if a filter portionsuch as a Ge layer is not provided on the cap body 20, it is notnecessary to enclose the switching transistor 30 (particularly drainregion) with the cap body 20.

[0111] Embodiment 1

[0112] Next, description will be made for an embodiment 1 applying theelectronic device according to the invention to a discrete type ofinfrared sensor.

[0113]FIGS. 4A and 4B are a cross-sectional view and an electricalcircuit for illustrating an infrared sensor according to Embodiment 1 ofthe invention, respectively.

[0114] As shown in FIG. 4A, the infrared sensor of the presentembodiment comprises a Si substrate 110 having a thickness of 300 μm, aresistance element (bolometer) 120 provided on the Si substrate 110, aswitching transistor 130 provided on the Si substrate 110 for turning onand off a current to the resistance element 120, and a cap body 140 forholding the area having the resistance element 120 placed thereon in anatmosphere of reduced pressure. The total size of this infrared sensoris about several mm. Above the Si substrate 110, there are provided theresistance body 111 patterned into a fanfold (Z-fold)-shape, a siliconnitride film 112 and a silicon oxide film 113 supporting the resistancebody 111, a BPSG film 116 and a passivation film (silicon nitride film)117 covering the resistance body 111. The silicon oxide film 113, BPSGfilm 116 and silicon nitride film 112 are patterned into a fanfold-shapetogether with the resistance body 111, and extend to above the siliconsubstrate 110. Cavity portions 119 and 143 held under vacuum areprovided below and above the fanfold-shape-like resistance body 111,silicon oxide film 113, BPSG film 116, and passivation film 117,respectively. The cavity portions 119 and 143 are connected with eachother through a gap and a side space in the region where the siliconoxide film 113, BPSG film 116 and silicon nitride film 112 areintegrated. Thus, the whole of the resistance body 111, silicon oxidefilm 113, BPSG film 116, passivation film 117, and silicon nitride film112 is constructed in the fanfold-shape to hang across above the cavityportion 119.

[0115] The materials of the resistance body 111 may include Ti, TiO,polycrystalline silicon, Pt or the like, and both of them can be usedtherefor.

[0116] Also, a ring-shaped film 118 made of a soft metallic material(such as aluminum) is provided on the region of the passivation film 117which is located below the drum portion 142 of the cap body 140, andalso a ring-shaped film 144 of a soft metallic material (such asaluminum) is provided on the end of the drum portion 142. Thus, thering-shaped joining portion 15 formed between both the joining portions118 and 142 holds the cavity portions 119 and 143 existing between thecap body 140 and the Si substrate 110 in an atmosphere of reducedpressure (vacuum). That is, by the existence of the cavity portion 119and 143, the resistance body 111 is configured to be thermally insulatedfrom the Si substrate 110, thereby maintaining a high efficiency ofconverting from infrared radiation to heat.

[0117] Also, the substrate portion 141 of the cap body 140 areconfigured by a Ge layer having a thickness of about 3 μm and a Si layerhaving a thickness about 1 μm epitaxially grown on a silicon substratehaving a thickness of about 300 μm, in which the surface of the Si layeris shaped into a Fresnel lens. The drum portion 142 of the cap body 140forms a cavity portion having a depth more than several μm. By the way,A region of the cap body corresponding to a window portion may be madethinner by etching or the like.

[0118] Also, the switching transistor 130 has the source region 131,drain region 132, and gate electrode 133. Thus, the drain region 132 isdisposed below the drum portion 142 of the cap body 140, and the drainregion 132 is configured to function as wiring for communicating signalsbetween the resistance body 111 sealed under vacuum and an externalmember.

[0119] Further, although not shown in FIG. 4A, a Peltie element forcooling the resistance element is mounted on the lower surface of the Sisubstrate 110. This Peltie element uses heat-absorbing actionaccompanying the movement of carriers passing through a Schottky contactportion. In this embodiment, various Peltie elements having well-knownstructures may be used.

[0120] As shown in FIG. 4B, one end of the resistance body 111 isconnected to the wiring 135 for feeding a power supply voltage Vdd, andthe other end of the resistance body 111 is connected to the drainregion 132 of the switching transistor 130. Also, an ON-OFF switchingsignal is input to the gate of the switching transistor 130 through thewiring 136, and the source of the switching transistor 130 is connectedto a detection portion (not shown) for detecting the amount of infraredradiation received by the resistance body 111 through wiring 138, theother end of which connected to a standard resistance. Further, thesubstrate region of the switching transistor 130 is connected to groundfor feeding a ground voltage Vss through wiring 137. That is, when thetemperature of the resistance body 111 changes according to the amountof infrared radiation and thus its resistance value also changes, thepotential of the wiring 138 changes and thereby the amount of infraredradiation is detected from an change in the potential.

[0121] On the other hand, for a discrete type of infrared sensor, anoperational amplifier for amplifying output from a bolometer may beprovided on the substrate, as well. In this case, the operationalamplifier may be positioned on the region sealed by the cap body inaddition to the bolometer and switching transistor of the presentembodiment.

[0122] Next, one example of a process for manufacturing the infraredsensor according to the invention will be described. FIGS. 5A to 5F arecross-sectional views for showing process steps for manufacturing theinfrared sensor according to Embodiment 1 (see FIGS. 4A, 4B) of theinvention. Also, FIGS. 6A to 6E is a plan view for showing process stepsfor forming a bolometer and the peripheral region thereof. Then, FIG. 5Ais a cross-sectional view taken along a line Va-Va shown in FIG. 6C,FIG. 5B is a cross-sectional view taken along a line Vb-Vb shown in FIG.6D, and FIG. 5D is a cross-sectional view taken along a line Vd-Vd shownin FIG. 6E.

[0123]FIG. 13 is a cross-sectional view for showing the whole structureof the infrared sensor according to the invention. As shown in the samefigure, the infrared sensor comprises a sensor region Rsens configuredas disposing cell regions having a resistance element such as abolometer and a switching transistor in a array-like arrangement, and aperipheral circuit region Rperi (control circuit) configured asdisposing transistors for controlling current and operation of the cellregion (see FIG. 9). However, in the present embodiment, only thechanges of structure of the sensor region Rsens in the manufacturingprocess will be described. The changes of structure of the peripheralcircuit region Rperi in the manufacturing process are independent of thecharacteristics of the invention, and various well-known CMOS processesmay be used therefor.

[0124] First, in the process step shown in FIG. 5A, a flat plate-likesilicon nitride film having a large number of openings 112 x as shown inFIG. 6A is formed on the Si substrate 110. Next, the silicon substrate110 is dry-etched using this silicon nitride film 112 as a mask to formholes with the bottoms directly below the openings 112 x, and thereafterthe holes are wet-etched to be enlarged in the vertical and lateraldirections. Thereby, cavity portions 119 x having a depth of about 1 μmare formed as shown in FIG. 6B. At this time, FIG. 5A shows that a wallportion 110 x exists between adjacent small cavity portions 119 xwithout exception, but the holes 112 x closed to each other may bejoined together in the lower portion thereof to form relatively largecavity portions.

[0125] Then, when a polycrystalline silicon film 113 is formed on thesilicon nitride film 112, the polycrystalline silicon film 113 does notcompletely cover the holes 112 x, so that small openings 113 x also areformed in the polycrystalline silicon film 113, as shown in FIG. 6C.

[0126] Next, in the process step shown in FIG. 5B, the polycrystallinesilicon film 113 is thermally oxidized to form a silicon oxide film 113a, and thus the openings 113 x are closed by the silicon oxide film 113a. Further, after a resistance body film of a conducting material suchas Ti is deposited on the silicon oxide film 113 a, this film ispatterned, thus forming a resistance body 111 having a fanfold-shape asshown in FIG. 6D.

[0127] After that, after depositing a polycrystalline silicon film onthe substrate, the polycrystalline silicon is patterned to form the gateelectrode 133. Then, impurity atoms (for example, n-type impurity atomssuch as arsenic and phosphorus) are implanted into the region positionedalong both sides of the gate electrode 133, thus forming the sourceregion 131 and drain region 132.

[0128] At this time, MIS transistors in the peripheral transistor region(not shown) except for the sensor region are also formed at the sametime. After that, although not shown, several layers of interlayerinsulating films and wiring layers (that is, multi-layer wiring layers)are formed on the substrate to cover members already formed in thesensor region and the transistor region. However, in the presentembodiment, the wiring layer is not formed in this process step and onlyseveral layers of interlayer insulating films are deposited in thesensor region.

[0129] Next, in the process step shown in FIG. 5C, a silicon oxide film116 is deposited on the interlayer insulating film of the sensor regionto cover the whole upper surface of the substrate including the gateelectrode 133 and the resistance body 111.

[0130] Next, in the process steps shown in FIG. 5D and FIG. 6E, the partof the silicon oxide 116 located in the gap portions of the resistancebody 111 is removed. At this time, part of the silicon oxide film 116remains covering the resistance body 111. After that, a passivation film117 of silicon nitride is deposited on the substrate. The passivationfilm 117 is to prevent water and moisture from entering into theresistance body 111 and the switching transistor 130. After that, it isperformed to remove the portions of the passivation film 117, siliconoxide film 113, and silicon nitride film 112 that are located in the gapportions of the resistance body 111. Thereby, the forming of a bolometer120 is completed. At this time, the wall portions 110 existing betweenthe cavity portions 119 x are also removed, and thus a large cavity 119is formed. Then, the cavity portion 119 communicates with external spacethrough openings Het formed by this etching. Also, the resistance body111 remains packaged by the silicon oxide film 113, silicon oxide film116, and passivation film 117.

[0131] On the other hand, in the peripheral transistor region not shown,the passivation film 117 may be formed to cover the top layer of themulti-layer wiring. This passivation film is extremely commonly formedin the processes of manufacturing LSI's. In the embodiment, thepassivation film 117 of the sensor region can be formed of the samesilicon nitride film as the passivation film covering the peripheraltransistor region in common process steps.

[0132] Next, in the process step shown in FIG. 5E, a ring-shaped film118 of metal (aluminum (Al)) having a thickness of 600 nm and circularlyenclosing the resistance body 111 and the switching transistor 130 isformed on the part of the passivation film 117 located in the peripheralregion of the resistance body 111. At this time, part of the ring-shapedfilm 118 is positioned above the source region 131 of the switchingtransistor 130.

[0133] Also, although not shown in FIG. 5E, the wiring 51 a-51 e asshown in FIGS. 3A and 3B are formed. That is, after contact holes areformed so as to pass through the passivation film 117 and silicon oxidefilm 116 to reach the impurity-diffused layers (including the source anddrain regions) and the bolometer resistance body 111, the wiring isformed to fill the contact holes and to extend on the passivation film.

[0134] Next, in the process step shown in FIG. 5F, a cap body 140 isprepared on a silicon substrate, where the cap body has a substrateportion 141 to provide a window for transmitting infrared radiation inthe wavelength range not shorter than 1.4 μm, a drum portion 142enclosing a recess portion and a ring-shaped film 144 of Al provided onthe end of the drum portion 142. Then, by aligning the ring-shaped film144 on the cap body 140 and the ring-shaped-film 118 on the Si substrate110 to each other, both of them are joined to each other to form thering-shaped joining portion 15. At this time, the whole cell region havenearly the same plane shape and circuit structure as shown in FIGS. 3Aand 3B, respectively.

[0135] Herein, each ring-shaped film 118, 144 is formed by patterning anAl film deposited by sputtering. Then, after the ring-shaped films 118and 144 are subjected to FAB (First Atom Beam) processing, that is,irradiated with Ar atoms, to expose dangling bonds on their surface,both films are joined to each other by pressure bonding. The detailedprocess of this joining will be described later.

[0136] Further, in the embodiment, although the description has beenmade particularly for the process steps for manufacturing an infraredsensor in which a resistance body called a bolometer is used, methodswhich can use the invention for forming a bolometer is not limited tothese process steps for manufacturing. Also, the method can use anothertype of infrared sensor. In this case, a completely different processfor manufacturing will be used. Whatever the case may be, since thecharacteristic of the invention is not for the structure of bolometersthemselves, it will be omitted to describe the process steps ofmanufacturing where the invention is applied to another type of infraredsensor, a pressure sensor, and acceleration sensor.

[0137] Hereinbefore, according to the process steps of manufacturingshown in FIGS. 5A to 5F, the two following advantages are obtained.

[0138] First, in the process steps shown in FIG. 5D and FIG. 6E, thewall portions 110 x existing between the cavity portions 119 x are alsoremoved to form a large cavity 119. Thus, pillars and walls connectingthe upper resistance element 120 and the lower substrate region do notexist in the cavity portion 119, and therefore heat dissipation of theresistance element 120 can be made as little as possible, therebypermitting improvement of the detection sensitivity and detectionaccuracy of the infrared sensor.

[0139] Second, because the cavity portion 119 formed below theresistance element 120 communicates with the space within the cap 141through the hole Het, the atmosphere of the cavity portion 119 has thesame degree of vacuum as the atmosphere in the cap 141. That is, if thecavity portion 119 is isolated, the cavity portion 119 is sealed underthe atmosphere in the oxidation step shown in FIG. 5B, and thus it isimpossible to maintain the cavity portion 119 under a relatively highdegree of vacuum. In contrast to this, in the embodiment, the degree ofvacuum of the cavity portion 119 is the same as the degree of vacuumwithin the cap body 140, that is, the degree of vacuum when thering-shaped joining portion 15 of the cap body 140 is formed (forexample, a degree of vacuum in the range of approximately 10⁻² Pa-10⁻⁴Pa). Therefore, it is possible to suppress thermal radiation from theinfrared sensor, thereby permitting improvement of the detectionsensitivity and detection accuracy of the infrared sensor.

[0140] However, in stead of removing all of the wall portions as in theembodiment, the wall portions and pillars may be partially remained. Inthis case, the advantages of forming the ring-shaped joining portion 15by means of metallic bonds and hydrogen bonding, and the advantages ofindividually providing the cap bodies for each cell region can beexerted, as well.

[0141] Also, no mutual communication between the spaces of the cavityportion 119 and the cap body 140 may be possible. In this case, theadvantages of forming the ring-shaped joining portion 15 by means ofmetallic bonds and hydrogen bonding, and the advantages of individuallyproviding the cap bodies for each cell region can be exerted, as well.

[0142] —Method for Forming Cap Body—

[0143]FIGS. 7A to 7F are cross-sectional views for showing a method forforming the cap body used in the electronic device according to thepresent embodiment.

[0144] First, in the process steps shown in FIG. 7A, a cap wafer 150 isprepared by epitaxially growing a Ge layer and a Si layer on a siliconwafer in sequence. For epitaxial growth of a Ge layer having a thicknessof about 3 μm on a silicon wafer, after a Si_(1-x)Ge_(x) layer is grownon the silicon wafer such that the Ge component ratio x may change from0 to 1 as described above, a Ge layer having a predetermined thicknessis epitaxially grown on the Si_(1-x)Ge_(x) layer. Further, after that,after a Si_(1-x)Ge_(x) layer is grown on the Ge layer such that the Gecomponent ratio x may change from 1 to 0, a Si layer having a thicknessof about 1 μm is epitaxially grown on the Si_(1-x)Ge_(x) layer. Then, aFresnel lens to provide a convex lens for focusing infrared on eachinfrared sensor are formed on the surface of the Si layer.

[0145] Then, in a state where the Fresnel-lens-formed side of the capwafer 150 is pointed downward, as shown in FIG. 7A, an Al film 151having a thickness of about 600 nm is formed on the surface opposing tothe Ge and Si layers of the cap wafer 150 by an evaporation method andsputtering method.

[0146] Next, in the process step shown in FIG. 7B, a resist pattern (notshown) is formed on the Al film 151, and the Al film 151 is etched usingthe resist pattern as a mask, forming a ring-shaped film 144.

[0147] Then, in the process step shown in FIG. 7C, using the ring-shapedfilm 144 as a mask (hard mask), or with the resist pattern left,dry-etching (RIE) is performed to form a drum portion 142 enclosing arecess portion, which provides a cavity for each infrared sensor, on thecap wafer 150. At this time, the cap wafer 150 is configured by asubstrate portion 141, having the remaining of the silicon wafer, the Gelayer, Si layer, Fresnel lens, etc., and a drum portion 142. Herein, theheight of the drum portion 142 or the depth of the recess portion ismore than several μm.

[0148] Further, as a method for forming the cap body, a SOI substratehaving an insulating oxide layer (for example, a so-called BOX layer)may be used instead of a bulk Si substrate. In this case, since the Sisubstrate can be etched under the condition of a high selection ratio ofetching between the insulating layer and the Si substrate, the formingof a recess portion can be reliably stopped at the insulating layer.

[0149] Next, in the process step shown in FIG. 7D, in the state wherethe substrate portion 141 of the cap wafer 150 is pointed upward, adepth of cut 152 is formed into the substrate portion 141 of the capwafer 150 by dry etching using ICP-RIE. The depth of cut is used forseparating the substrate potion 141 to form an individual cap body foreach infrared sensor. Next, a main body substrate 100 having a structuresuch as shown in FIG. 5F and FIG. 3A is prepared, and a ring-shaped film118 of Al having a shape such as shown in FIG. 5F and FIG. 3A is formedon the main body substrate 100.

[0150] Next, in the process step shown in FIG. 7E, the cap wafer 150 isplaced on the main body wafer 100 on which an infrared sensor has beenformed, for example, through process steps shown in FIGS. 5A to 5E, andthus the ring-shaped films 118 and 144 are joined to each other. Thus, ajoining step by pressure bonding is performed for forming thering-shaped joining portions 15 such as shown in FIG. 5F.

[0151] Next, in the process step shown in FIG. 7F, the cap wafer isbroken along the depth-of-cut portion 152 in the cap wafer 150 into thesections of each infrared sensor, and at the same time, the main bodywafer 100 is cut away into the sections of each infrared sensor bydicing, thereby providing a discrete type of infrared sensor (see FIG.5F) configured by the Si substrate 110 and the cap body 140.

[0152] —Detailed Joining Process by Pressure Bonding—

[0153]FIG. 8 is a cross-sectional view for schematically showing theconfiguration of an apparatus used for pressure bonding. As shown in thesame figure, a chamber 160 is provided with a supporting member 161 forapplying a pressure for use in pressure bonding, a wide band rotary pump162 for holding vacuum on the inside of the chamber 160, and irradiationequipment 163 and 164 for irradiation with Ar. Thus, in a state wherethe main body wafer 100 is placed above and the cap wafer 150 is placedbelow, the irradiation equipment 163, 164 irradiates each ring-shapedfilms 118 and 144 (see FIG. 7D) with Ar atom beams, respectively. Bythis processing, contaminants and oxide films are removed from thesurface of the Al films constituting the ring-shaped films 118 and 144.After that, while the degree of vacuum in the chamber 160 is being heldin a level of 10⁻⁴ Pa, a push pressure of 0.5 MPa-20 MPa is appliedbetween the ring-shaped films 118 and 114 at room temperature (forexample, about 30° C.). Thereby, the ring-shaped films 118 and 144 arejoined to each other.

[0154] At this time, by heating the ring-shaped films 118 and 144 atabout 150° C. before pressure bonding, Ar atoms absorbed on the surfacemay be driven out.

[0155] Also, instead of the irradiation with Ar atoms, the irradiationwith O atoms and other neutral atoms may be used to expose danglingbonds on the surface of the metal, thereby providing the same advantagesas in the embodiment.

[0156] As metals used for the joining, other metals (including alloys)than Al can be used. Particularly, by using In, Cu, Au, Ag, and Al—Cualloy having low melting points, the joining can be performed at roomtemperature or at low temperature near room temperature. A set of thesame metals or a set of different metals among these metals may be usedfor the joining.

[0157] For example, when a In film is formed by evaporation as thering-shaped film, the surface of the In film is crushed by applying apressure thereto, and thus natural oxide films existing on the surfaceare also crushed. Thus, metallic bonds can be established between the Inlayers. Such pressure bonding may be used, as well.

[0158] Also, the joining method is not limited to thermal pressurebonding, and there are the use of ultrasonic joining and a method forestablishing the joining by providing plastic deformation at roomtemperature. Either of them may be used. Further, The use of Si—Si,Si-oxide film, and oxide film-oxide film hydrogen bonding may be alsopossible.

[0159] Particularly, when the joining is made at a degree of vacuum inthe range of 10⁻² Pa-10⁻⁴ Pa, the function of a infrared sensor or thelike can be maintained relatively high due to a high degree of vacuum inthe internal space, and at the same time, it is possible to avoiddifficulty of holding a high vacuum, thus permitting the joining whichis practical and suitable for mass production.

[0160] According to the embodiment, a whole cell array including manyelements such as sensors, emitting elements or the like is not holdunder vacuum, in contrast to the conventional devices described above.Using a wafer having a large number of infrared sensors formed therein,it is possible to individually seal each infrared sensor in a vacuum.Therefore, the embodiment is easily applicable for a discrete type ofelement.

[0161] Particularly, the embodiment can use a process for manufacturingelectronic devices, particularly, CMOS process as it is, and thus itprovides a practical manufacturing method.

[0162] Also, the embodiment does not form the sealing portion by thesolder joining as in conventional technologies, but forms the sealingportion by using the joining between soft metals such as aluminum.Therefore, it is easily applicable to miniaturization of elements suchas an infrared sensor.

[0163] Also, the process steps of manufacturing according to theinvention can join individually a cap body to each infrared sensor, evenin the case of forming a large number of infrared sensors of a discretetype on a wafer. Particularly, as shown in FIG. 7D, by forming thedepth-of-cut portion 152 into the substrate portion 141, stress appliedto the joining portion can be made uniform for each cell, and thus largelocal stress does not work during joining, thereby the reliability ofthe joining portion being improved.

[0164] Embodiment 2

[0165]FIG. 9 is an electrical circuit for illustrating the configurationof an infrared area sensor according to Embodiment 2 of the invention.The concrete structure of the infrared area sensor according to thepresent embodiment is shown in FIG. 13.

[0166] As shown in the same drawing, a main body substrate is providedwith a cell array in which a large number of cells A1-E5 each having abolometer 201 and a switching transistor 202 are disposed in matrix-likearrangement. Although the size of one cell is, for example, about 40μm-50 μm, the size is adequate to be larger than 20 μm corresponding toabout two times the wavelength of infrared radiation to be detected. Thegate electrodes of the switching transistors 202 in each cell areconnected to selection lines SEL-1-SEL-5 extending from a verticalscanning circuit 209 (V-SCAN). One end of the bolometer 201 in each cellis connected to a power supply line 205, the sources of the switchingtransistors 202 are connected to data lines 204 a-204 e extending fromground through reference resistors Ra-Re. Also, the data lines 204 a-204e are connected to an output amplifier 206 through switching transistorsSWa-Swe, respectively. Signal lines 207 a-207 e extending from ahorizontal scanning circuit 208 (H-SCAN) are connected to the gateelectrode of each switching transistor SWa-SWe.

[0167]FIG. 10 is a timing chart for showing a method for controlling theinfrared area sensor according to the embodiment. When the selectionline SEL-1 is driven by the control from the vertical scanning circuit(V-SCAN), the switching transistors 202 in each of the cells A1-E1 turnon, and the bolometers 201 are supplied with voltages through thereference resistors Ra-Re. On the other hand, the switching transistorsSWa-SWe are sequentially driven from the horizontal scanning circuit(H-SCAN), and thus data Da1-De1 from each of the cells A1-E1 are outputfrom the output amplifier 206. Next, when the selection line SEL-2 isdriven according to the control from the vertical scanning circuit(V-SCAN), the switching transistors SWa-SWe are sequentially drivenaccording to the control from the horizontal scanning circuit (H-SCAN)and thus data Da2-De2 of each of the cells A2-E2 are output from theoutput amplifier 206. Similarly, according to the control of thevertical scanning circuit (V-SCAN) and the horizontal scanning circuit(H-SCAN), data Da3-De3 of each of the cells A3-E3, data Da4-De4 of eachof the cells A4-E4, and data Da5-De5 of each of the cells A5-E5 aresequentially output from the output amplifier 206.

[0168] Thus, input levels of infrared radiation in the cells in whicheach bolometer 201 are disposed are collected, thereby providing twodimensional information with respect to a detection target.

[0169]FIGS. 11A to 11F are perspective views for showing process stepsfor manufacturing an infrared area sensor having the cell arrayaccording to the embodiment.

[0170] The process steps shown in FIGS. 11A to 11E perform the sameprocessing as the process steps shown in FIGS. 7A to 7E in Embodiment 1described above.

[0171] Thus, in the process step shown in FIG. 11F, by breaking a capwafer 150 along a depth-of-cut portion 152, an infrared area sensorhaving a cap body 140 placed on each cell of the cell array is provided.

[0172] Herein, the remaining thickness at the depth-of-cut portion 152may be adjusted such that the breaking shown in FIG. 11F can occur onapplication of pressure bonding force for joining. Also, the breakingmay be done by separately applying push pressure to the depth-of-cutportion 152 after the completion of the joining by pressure bonding.

[0173] By the way, since the infrared area sensor shown in FIGS. 11A to11F is basically similar to that shown in FIGS. 7A to 7F, the samesymbols are used in them. However, generally, the cells in a discretetype of device and the cells in an integration type of device aresubstantially different in size.

[0174] In conventional technologies, it has been impossible to realizean electronic device having a vacuum dome with dimensions of a diameter(or a side) less than several hundreds μm and a height less than severalhundreds μm. In contrast, the present embodiment allows forming suchdevice. In this case, the wall of the drum portion of the cap body has athickness less than several tens μm and the ceiling thereof has athickness less than several hundreds μm. Particularly, a vacuum dopehaving the dimension of a diameter (or a side) less than several tens μmand a depth less than several μm may be called “μ vacuum dome”. Also, atechnology for forming this vacuum dome requires joining ring-shapedfilms having a thickness of sub-micron to each other, and therefore itmay be called “nano-joining vacuum dome”.

[0175] Also, in the case of the infrared sensor having a cell array, themain body wafer 100 is provided with a bolometer, wiring for making eachcell to cell connection, an electronic circuit, or the like, but therepresentation of them are omitted in FIGS. 11A to 11F. Further,generally, since the infrared area sensors having a cell array areformed more than one in number on a wafer, after the process step shownin FIG. 11F, the main body wafer 100 is broken into each chip by dicingor the like.

[0176] The embodiment can provide the following advantages.

[0177] First, in the case where the region of a large area containingthe whole of a cell array is sealed by one cap as in conventionaltechnologies, a large force of pressure bonding is sometimes locallyapplied to a joining portion during pressure bonding for joining, andthus the joining portion can be destroyed and the substrate can bebroken. In contrast, if each cell is individually joined to a cap bodyas in the embodiment, the stress applied to each joining portion duringjoining by pressure bonding can be made uniform by the depth-of-cutportion 152 provided in the cap wafer 150 as shown in FIG. 11. At thistime, the cap wafer may be configured to be naturally broken along thedepth-of-cut portion by the force of pressure bonding for joining. Thatis, it is possible to prevent the occurrence of an excessively largelocal stress, thereby permitting an improvement in reliability duringjoining, during process steps thereafter, or during practical use.

[0178] Second, in the case where a whole cell array is sealed in a capbody as in conventional infrared sensors, if a junction failure occursat part of the joining portion, the whole of the cell array becomesdefective and it is almost impossible to provide saving thereto. Incontrast, according to the present embodiment, in an electronic devicein which a large number of cells each having an element such as aninfrared sensor disposed therein are arranged in an array likearrangement, each cell is configured to have a cap body for vacuumsealing. Therefore, even if part of the cells cannot be held under anormal vacuum due to a junction failure in the joining portions thereof,the saving for the defectives can be performed by taking measures forusing information of the normal cells adjacent to the defective cells.

[0179] Third, in the case where the region of a large area containingthe whole of a cell array is sealed by one cap body as in conventionaltechnologies, when the area of the cell array are particularly large,and when the window portion of the cap body is thin, a deflection can bedeveloped in the window portion due to a pressure difference between theatmosphere of reduced pressure within the cap and the external air.Therefore, there are fears that the window portion can be destroyed andthat the window portion can come into contact with the cell. Incontrast, in the present embodiment, since each cell is provided with acap body having a small area, such problems can not arise. As a resultof this, the window portion can be made thin in thickness to increasethe detection sensitivity for infrared radiation, and further the devicecan be made smaller.

[0180] Embodiment 3

[0181]FIG. 12 is a cross-sectional view for showing an example of amicro vacuum transistor having a vacuum dome structure according toEmbodiment 3 of the invention. The micro vacuum transistor according tothe present embodiment comprises a sapphire substrate 201, an n-GaNlayer 202 provided on the sapphire substrate 201 and functioning as anelectron supplying layer, an Al_(x)Ga_(1-x)N layer 203 provided on n-GaNlayer 202 and configured as a composition gradient layer havingcomposition approximately continuously changed and functioning as aelectron drift layer, an AlN layer 204 provided on the Al_(x)Ga_(1-x)Nlayer 203 and functioning as a surface layer, a lower electrode 205provided on the n-GaN layer 202, a surface electrode 206 provided on theALN layer 204 and forming a Schottky contact with the AlN layer 204, anda first insulating film 207 provided on the AlN layer 204 and having anopening portion. Further, a thin film portion 206 a of the surfaceelectrode 206 is formed on the region extending from the surface of theALN layer 204 exposed at the bottom plane of the opening portion of thefirst insulating film 207 to the upper surface of the first insulatingfilm 207 via on the side surface of the opening portion of the firstinsulating film 207. The thin film portion 206 a of the surfaceelectrode 206 is made of thin metal (such as Cu) having a thickness ofabout 5-10 nm, and the portion of the thin film portion 206 a formingSchottky contact with the AlN layer 204 in the opening portionconfigures an electron emitting portion. Further, a thick film portion206 b of the surface electrode 206 is made of metal having a thicknessof not less than 100 nm, and provided on the first insulating film 207,and connected to the thin film portion 206 a to function as a contactpad portion of wiring.

[0182] Then, a cap body 208 having a drum portion enclosing a vacuumdome 210 is provided on the first insulating film 207, and an upperelectrode 209 a for collecting electron is provided on the inner surfaceof the ceiling portion of the cap body 208. Further, an externalelectrode 209 b is provided on the outer surface of the ceiling portionof the cap body 208, and the upper electrode 209 a and the externalelectrode 209 b are connected to each other through a through-holepassing through the ceiling portion of the cap body 210. Also, apassivation film 211 of silicon nitride covering the surface electrode206, a ring-shaped film 212 of Al formed on the passivation film 211,and a ring-shaped film 213 formed on the end portion of the drum portionof the cap body 208 are provided. Thus, the ring-shaped films 212 and213 are joined to each other by pressure bonding to form the ring-shapedjoining portion 15. Further, the vacuum dome 210 has an inner diameterof about 10 μm and the pressure therein is a reduced pressure of theorder of 10⁻⁴ Pa.

[0183] In addition, the Al_(x)Ga_(1-x)N layer 203 has a content ratio ofAl to Ga is approximately 0 (x=0) in the lower end portion thereof and,conversely, has an Al content ratio of about 1 in the upper end portion.

[0184] In this vacuum transistor, electrons emitted according to signalsapplied between the surface electrode 206 and the lower electrode 205are accelerated in an electron travel chamber 210 and received by theupper electrode 209. Because the electron travel region is held undervacuum, the vacuum transistor can function as amplifying element or aswitching element having high insulating properties, low internal loss,and low temperature dependence.

[0185] Embodyment 4

[0186] In each embodiment described above, the structures described havea cap body provided individually for each cell region, but the inventionis not limited to such embodiments.

[0187]FIG. 14 is a cross-sectional view for showing the whole structureof an infrared sensor according to a fourth embodiment of the invention.As shown in the same figure, according to the present embodiment, thecap body does not cover each cell in the unit of a cell region, butcovers a plurality of cell regions in the sensor regions Rsens. Thus,the ring-shaped joining portion encloses the plurality of sensorregions. The materials of the cap body, and the materials and methodsfor configuring the ring-shaped joining portion are the same as inEmbodiment 1.

[0188]FIG. 15 is a cross-sectional view for showing an infrared sensoraccording to an example variation of the fourth embodiment 4 of theinvention. As shown in the same figure, according to the presentembodiment, the cap body does not cover each cell individually, butcovers all cell regions in the sensor region Rsens. Thus, thering-shaped joining portion encloses the whole sensor region Rsens. Thematerials of the cap body, and the materials and methods for configuringthe ring-shaped joining portion are the same as in Embodiment 1.

[0189] According to the present embodiment or the example variation, thering-shaped joining portion is formed by the joining using metallicbonds or hydrogen bonding or the room temperature joining, in contrastto conventional methods using solder. Thus, it is possible to maintain ahigh degree of vacuum in the space in which resistance elements aresealed, thereby permitting a more improvement in the detectionsensitivity and an improvement in detection accuracy of various sensorssealed in the cap body.

[0190] Other Embodiments

[0191] In each embodiment described above, the description has beenperformed for the case where the element held in an atmosphere ofreduced pressure are a bolometer and vacuum transistor, but theinvention is not limited to these embodiments. It is applicable to theentire elements requiring an atmosphere of reduced pressure or anatmosphere of inert gas, for example, a thermoelectric transducer exceptfor a bolometer such as a PN junction diode or the like, an element fordetecting or emitting a terameter wave having a wavelength of 40 μm-50μm, or the like.

[0192] Further, in each embodiment described above, the recess portionfor configuring a cavity portion and the closed-loop-like drum portionfor enclosing the cavity portion are provided only in the cap body, butthe invention is not limited to such embodiments. Both of the cap bodyand the main body substrate may have the recess portion for configuringa cavity portion and the closed-loop-like drum portion for enclosing thecavity portion. In this case, the cap body may be shaped like a flatplate.

[0193] Also, the shape of the drum portion enclosing the cavity portionmay be tubular and of a polygonal hollow structure such as a hollowrectangular structure. However, to maintain the cavity portion in anatmosphere of reduced pressure, they need to have a closed-loop circularstructure.

[0194] Further, it is possible to use a structure having only a recessportion provided in the flat main body substrate and not having a drumportion. In this case, the cap substrate may be shaped like a flat plateor may have a recess portion.

[0195] Further, it is possible to use a structure having only a recessportion provided in a flat cap-substrate and not having a drum portion.In this case, the main body substrate may be shaped like a flat plate ormay have a recess portion.

[0196] Also, in each embodiment described above, the cavity portionsealed by the cap body is assumed to be a vacuum dome. In this case, inviews of joining the ring-shaped film by pressure bonding performedduring the manufacturing process step, preferably the the cavity portionis approximately under a pressure of 10⁻² Pa-10⁻⁴ Pa, but it is possibleto perform the joining at a pressure not greater than 10⁻⁴ Pa andreaching to 10⁻⁷ Pa.

[0197] Also, the invention is applicable to a plasma light-emittingelement. The invention can be applied to a plasma light-emitting elementhaving a particular atmosphere containing a given gas (for example,helium gas, argon gas, neon gas, xenon gas, krypton gas, hydrogen gas,oxygen gas, nitrogen gas, etc.) and having an atmosphere of a reducedpressure not greater than 133 Pa, as long as the joining can beperformed by pressure bonding.

[0198] Also, in the plasma light-emitting element described, the capbody of the invention may be configured a material other thansemiconductor. For example, by configuring the cap body with atransparent material such as an oxide film and a silicon nitride film,it is possible to provide a device in which a light-emitting elementemitting visible light is sealed in an atmosphere of reduced pressure.At the time of using this structure, after deposition of a transparentinsulating film or the like on a Si substrate, a drum portion enclosinga recess portion not reaching to the Si substrate (here, the outsidesurface of the drum portion may reach to the Si substrate) is formed onthe transparent insulating film. Then, it is possible to place atransparent cap body on each cell in a procedure in which a cap body issealed for each cell on the main body substrate according to the joiningmethod described in each above embodiment, and then only the Sisubstrate is removed by dry etching or the like.

What is claimed is:
 1. An electronic device, comprising: a main bodysubstrate having a plurality of cell regions in which at least oneelement is disposed; a cap body placed on said main body substrate; acavity portion provided in a position having said element disposedtherein and being located in at least one cell region of said pluralityof cell regions, enclosed by said main body substrate and said cap bodyto be maintained in an atmosphere of reduced pressure or in anatmosphere of inert gas; and a ring-shaped joining portion providedbetween said main body substrate and said cap body for isolating saidcavity portion from external space.
 2. The electronic device accordingto claim 1, further comprising: a first ring-shaped film formed on saidmain body substrate and enclosing said element; and a second ring-shapedfilm formed on said cap body, wherein said ring-shaped joining portionis formed between said first and second ring-shaped films.
 3. Theelectronic device according to claim 2, wherein the materials of saidfirst and second ring-shaped films are selected from at least any one ofAl, In, Cu, Au, Ag, Ti, W, Co, Ta, Al—Cu alloy, and an oxide film. 4.The electronic device according to claim 3, wherein the materials ofsaid first and second ring-shaped films are the same material with eachother.
 5. The electronic device according to claim 1, wherein said mainbody substrate is configured by semiconductor, and said element on saidmain body substrate and an external circuit are electrically connectedto each other through an impurity-diffused layer formed in said mainbody substrate to extend across said ring-shaped portion.
 6. Theelectronic device according to claim 1, wherein said cap body isprovided with a recess portion for forming said cavity portion and adrum portion enclosing the recess portion, and said main body substrateis provided with an engagement portion for engaging with said drumportion.
 7. The electronic device according to claim 1, wherein saidelectronic device is an element selected from any one of an infraredsensor, pressure sensor, acceleration sensor, rate-of-flow sensor andvacuum transistor.
 8. The electronic device according to claim 7,wherein said electronic device is a infrared sensor, and the elementprovided on said main body substrate is a thermoelectric transducerelement.
 9. The electronic device according to claim 8, wherein said capbody has a Si substrate and a semiconductor layer provided on the Sisubstrate and having a band gap of less than 1.1 eV.
 10. The electronicdevice according to claim 8, wherein the top layer of said cap body isconfigured by a Si layer having a diffraction pattern formed thereon toprovide a Fresnel lens.
 11. The electronic device according to claim 7,wherein said electronic device comprises an infrared sensor having athermoelectric transducer element, a support member for supporting saidthermoelectric element, and a second cavity portion formed below saidsupport member.
 12. The electronic device according to claim 11, whereinsaid second cavity portion is not provided with a pillar or a wallextending from said support member.
 13. The electronic device accordingto claim 11, wherein said second cavity portion is configured tocommunicate with said cavity portion.
 14. The electronic deviceaccording to any one of claims 1 to 13, wherein said ring-shaped joiningportion is provided more than one in number to enclose said plurality ofcell regions.
 15. A method for manufacturing an electronic device,comprising: a step (a) of preparing a main body substrate having aplurality of cell regions in which at least one element is disposed anda cap substrate, and forming a plurality of recess portions eachenclosing at least one cell region of said plurality of cell regions onat least any one of said main body substrate and said cap substrate; anda step (b) of forming a ring-shaped joining portion such that at leastpart of recess portions of said plurality of recess portions may remainas cavity portions isolated from external space between said main bodysubstrate and said cap substrate, by applying a push pressure betweensaid main body substrate and said cap substrate.
 16. The method formanufacturing an electronic device according to claim 15, wherein saidstep (a) includes preparing a plurality of first and second ring-shapedfilms enclosing said recess portions on said main body substrate and capsubstrate, respectively, and said step (b) includes forming saidring-shaped joining portion between said first and second ring-shapedfilms.
 17. The method for manufacturing an electronic device accordingto claim 15, wherein said step (b) is performed with the joining usinghydrogen bonding and a metallic bond or with room temperature joining.18. The method for manufacturing an electronic device according to claim16, wherein said step (a) is performed by using material selected fromat least any one of In, Cu, Al, Au, Ag, Ti, W, Co, Al—Cu alloy, and anoxide film as the materials of said first and second ring-shaped films.19. The method for manufacturing an electronic device according to claim18, wherein as the materials of said first and second ring-shaped films,the same material is used to both films.
 20. The method formanufacturing an electronic device according to claim 15, wherein saidstep (b) is performed without heating said main body substrate and saidcap substrate to a temperature of not less than 450° C.
 21. The methodfor manufacturing an electronic device according to claim 15, whereinsaid step (a) includes forming a slit for partitioning said capsubstrate into a plurality of areas in said cap substrate.
 22. Themethod for manufacturing an electronic device according to claim 16,wherein said step (a) includes forming recess portions enclosed by saideach second ring-shaped film and a plurality of drum portions enclosingsaid recess portions on said cap substrate.
 23. The method formanufacturing an electronic device according to claim 22, wherein saidstep (a) includes forming an engagement portion for engaging with thedrum portion of said cap substrate in said main body substrate.
 24. Themethod for manufacturing an electronic device according to claim 15,wherein said step (b) is performed in an atmosphere of reduced pressure,or in an atmosphere of inert gas.
 25. The method for manufacturing anelectronic device according to claim 24, wherein said step (b) isperformed in an atmosphere of reduced pressure having a pressure ofhigher than 10⁻⁴ Pa.
 26. The method for manufacturing an electronicdevice according to claim 15, further including a step of breaking saidmain body substrate into each cell after said step (b).
 27. A method formanufacturing an electronic device, comprising: a step (a) of preparinga main body substrate having a plurality of cell regions in which atleast one element is disposed and a cap substrate, and forming a recessportion enclosing said plurality of cell regions in at least one of saidmain body substrate and said cap substrate; a step (b) of forming aring-shaped joining portion with the joining using hydrogen bonding or ametallic bond or with room temperature joining by applying a pushpressure between said main body substrate and said cap substrate,wherein in said step (b), said ring-shaped joining portion is formedsuch that at least a portion of said recess portions may remain as acavity portion isolated from external space in said plurality of cellregions.
 28. The method for manufacturing an electronic device accordingto claim 27, wherein said step (a) includes forming a first ring-shapedfilm enclosing a plurality of cell regions on said main body substrateand forming a second ring-shaped film having approximately the samepattern as said first ring-shaped film on said cap substrate.
 29. Themethod for manufacturing an electronic device according to claim 28,wherein said step (a) is performed by using material selected from atleast any one of In, Cu, Al, Au, Ag, Ti, W, Co, Al—Cu alloy, and anoxide film as the materials of said first and second ring-shaped films.30. The method for manufacturing an electronic device according to claim29, wherein as the materials of said first and second ring-shaped films,the same material is used to both films.
 31. The method formanufacturing an electronic device according to claim 27, wherein saidstep (b) is performed without heating said main body substrate and saidcap substrate to a temperature of not less than 450° C.
 32. The methodfor manufacturing an electronic device according to claim 27, whereinsaid step (a) is performed such that all cell regions disposed on oneelectronic device may be enclosed by said first and second ring-shapedfilms.